How Much is Too Much? Where is the Value in Attending Conferences?

After exploring on “Serge the Concierge”: http://www.sergetheconcierge.com the Consumed to Thrifty thread, I thought it could be useful to see how this applies to picking which conferences are worth attending, what their value proposition is.

Therefore I offer to have a session looking at this topic

What justifies attending a conference, an event? How much is too much as far as price goes? Does the time and place plays a role in your choice? Is face time with people you have only had contacts with online the best part. Where are the best spots to make new connections, the coffee line, lunch break? Have you felt that your time and money would have been spent better if you took a vacation instead of attending a certain event? Which? When? Where?